Anorectal malformations

Anorectal malformations are not uncommon. A child who has the misfortune to be born with one presents soon after birth with abdominal distension and the failure to pass meconium. Some lesions are incomplete, and present later with difficulty passing faeces, small faeces, or distension.

There are many kinds of lesion, but what matters most is whether a child's rectum ends above or below his puborectalis sling. If his rectum extends below it (infralevator lesions), you can make him an anus, or dilate a stenosed one without difficulty. But if his rectum ends above this sling (supralevator lesions), you will have to make a temporary colostomy, and refer him later for his sigmoid colon to be pulled through to his perineum. This is difficult, but continence can be achieved in most cases.

A child's anus or rectum may fail to develop entirely (agenesis), they may partly fail to develop (atresia), or his rectum or anus may be narrowed (stenosis). Agenesis (but not the other lesions) may be combined with fistulae between the rectum, and the urinary, or genital tracts, of either sex. These variables combine to produce a complex series of lesions. Some fistulae are useful, because you may be able to dilate them to make an anus. About 75% of cases are low lesions with fistulae.

Fig. 28-6 AN ''IMPERFORATE ANUS' showing high and low rectal lesions. The child has been turned upside down and a piece of metal has been placed over his anus. A, shows a high lesion with the gas bubble in his rectum, more than 2 cm from a coin which has been placed over his anus. B, is a low lesion in which the metal hub of a needle has been used, and is less than 2 cm from the gas bubble. The hub of a needle is better than a coin because it fits into the anal cleft.

LOW ANORECTAL LESIONS Anal stenosis in boys or girls (rare).

Imperforate anal membrane (3%) in boys and girls.

Low rectal (anal) agenesis without a fistula. If there is a fistula (75%), it is rectoperineal or rectourethral in a boy. In a girl it is rectoperineal, rectovaginal, or rectovulvar.

HIGH ANORECTAL LESIONS High rectal agenesis in boys or girls without a fistula (7%). If there is a fistula (15%), it is rectourethral or rectovesical in a boy. In a girl it is rectovaginal or rectocloacal.

Rectal atresia in boys and girls (rare and not discussed further). There is a normal looking anus in the normal place, low gut obstruction (no meconium, abdominal distension and vomiting late). A contrast enema is safter than probing.[+5]

You should be able to diagnose which kind of lesion a child has from the clinical signs and a simple X-ray (28-6). The risk in trying to repair an anorectal lesion is that, if the lesion is higher than you expect, you may so damage his rectal anatomy that even an expert cannot repair it later. If you find you are operating below skin level, stop, do a colostomy, and refer the child for repair later. Don't divide any muscle. If you are in any doubt, a colostomy would be wiser, even though you may occasionally do one unnecessarily. The penalty for failure is incontinence. Make a transverse colostomy rather than a sigmoid one, because it will make the secondary procedure easier, although it will cause more fluid loss.

Fig. 28-7 LOW RECTAL AGENESIS WITHOUT A FISTULA. A, make a cross-shaped incision over the child's external sphincter. B, reflect 4 skin flaps, and then cut interdigitating flaps from his anal membrane. C, close these so that they interdigitate with -one another. Adapted from Ravitch et al., ''Paediatric Surgery', Fig 98-3. Yearbook Medical, with kind permission.

ANORECTAL MALFORMATIONS If possible, refer these children, unless they need dilatation only.

EXAMINATION. Ask your midwives to examine the anuses of all children. Ask them to refer: (1) any child with an abnormal anus, (2) any child who passes no faeces for 12 hours, and whose abdomen distends. Examine him, and if necessary, pass a rectal thermometer or a stiff catheter. If he has no anus, an opening must be provided before he distends. Look for other congenital abnormalities.

If there is a mass of irregular epithelium where the anus should be, the diagnosis is almost certainly anal stenosis. Probe it and look for even a trace of meconium to confirm the presence of an anus.

If the anal skin is smooth, there must be some other kind of lesion, other than stenosis.

If there is a thin veil of epithelium overlying the anal orifice, surrounded by normal puckering and rugae, there is an imperforate anal membrane (only 3%).

If the anus looks normal, until you put a probe into it, when you find that the rectum is almost or completely blocked, the diagnosis is rectal atresia. You may find a very small hole which you can dilate.

LOOK FOR FISTULAE [s7]IN ANORECTAL MALFORMATIONS If a boy has low rectal (anal) agenesis, look for: (1) meconium in his urine. If you don't find it, he has probably not got a fistula. (2) Examine his perineum, and his perineal raphe along his scrotum. If you see any sign of a black head of meconium, he probably has a fistula leading to a low lesion.

If a girl has low rectal (anal) agenesis, examine her perineum and vulva for fistulae. If you find a suspicious opening, probe it gently[md]it may extend downwards and backwards under the skin of her perineal body, and confirm that she has a low lesion.

If a boy has high rectal agenesis, examine his urine for meconium.

If a girl has high rectal agenesis, look for a fistula on the posterior wall of her vagina, below her introitus. It may connect with a cloaca where her urinary tract, vagina, and rectum come together into a common channel.

X-RAYS [s7]FOR ANORECTAL MALFORMATIONS Wait until 12 to 16 hours after birth, when the gas the child has swallowed has reached the blind lower end of his gut.

Turn him upside down so that his anus is uppermost. Flex his knees. Strap a small piece of metal such as the metal adaptor of a needle flat on the skin where his anus should be.

Take a lateral film. The bubble of gas in his gut will be uppermost. The distance between it and the metal will show you how much tissue there is between the bottom of his gut and his skin.

Interpret the film in two ways: (1) If the gas bubble is less than 2 cm from his anus, he has a low lesion. If it is more than 2 cm from his skin, he probably has a high one. (2) Draw a line between the posterior part of his pubis, and the lowest segment of his sacrum. If any blind dilated bowel has gone beyond this line, he has a low lesion. If it remains above this line, his lesion is high.

CAUTION! (1) X-rays are useful but not completely reliable. There may not have been enough gas in his gut, or he may have a fistula higher up. (2) He may have a vesicorectal fistula and a fluid level in his bladder (uncommon). Exclude this by taking a supine lateral film.

OPENING A LOW LESION If a child has a low lesion, operate early, especially in a boy. His obstructed gut is going to distend, so, as soon as he has swallowed enough air to help make the X-ray diagnosis, pass a nasogastric tube. Keep him hydrated and give him vitamin K.

ANAESTHESIA. (1) Ketamine (A 8.5). (2) Chloral hydrate and local infiltation anaesthesia. (3) Awake tracheal intubation and general anaesthesia.

ASPIRATION. Immediately before you operate, aspirate his perineum with a syringe and large-bore needle. This will tell you the exact level of his anal pouch, while he is relaxed and anaesthetized.

CAUTION ! If you are in doubt, do a colostomy.

ANAL STENOSIS (boys and girls). If the opening is very small, use a filiform urethral catheter with a metal follower or the smallest Hegar dilator. Continue to dilate the child about every 2 weeks with your little finger. Later, this can be done by a nurse or the child's mother.

IMPERFORATE ANAL MEMBRANE (boys and girls). Incise the epithelial covering of the anus, and dilate it with a Hegar dilator. Continue to dilate it as above.

LOW RECTAL (anal) AGENESIS WITHOUT A FISTULA. Make a cross-shaped incision so as to mobilize four separate flaps, as in A, Fig. 28-7. Contributors then differ. One says: don't divide any muscle; if you don't immediately find the rectum under the skin, stop, make a colostomy and refer.

Another says: as soon as you have found the external sphincter, divide it at 12 o'clock, and dissect towards the blind end of the gut, up to 2 cm from the skin. Mobilize the blind gut for a few more centimetres, so that you can relax it, and bring it down to the skin within the cut external sphincter. Cut four triangular flaps, so that they interdigitate with the skin flaps. Join them with interrupted stitches of fine catgut (B, and C). Don't make the anastomosis under tension, if it is tight, you have not mobilized gut enough.

LOW RECTAL (anal) AGENESIS WITH A FISTULA IN A GIRL. This is the commonest anorectal lesion in a girl. Her sphincter muscles pass round the fistula. You can do two things: (1) is much the best; only do (2) if you cannot do (1).

(1) You can dilate her fistula until it makes an adequate anus. Start by using a rectal thermometer, and later a uterine sound. Then at 6 months, refer her to have her anus brought back to its proper place in her perineum. If this is impractical, it is not a disaster, but it will mean that she will always defecate from her fourchette. This is much less of a disability than it might seem, because it is compatible with a normal sex life, and her husband may be quite unaware of it!

(2) You can do a cutback operation, as in B, Fig. 28-8, but only if, before you cut, your scissors point directly backwards and are superficial. If they point in any other direction, and especially if they point deeply, she probably has a high lesion, not a low one, and she may subsequently become incontinent.

After you have cut, mobilize the posterior 180[de] of the cut, so as to bring the apex of the incision comfortably down to her skin. Join her gut and her skin with interrupted sutures.

LOW RECTAL (anal) AGENESIS WITH A FISTULA IN A BOY. His fistula is usually perineal, and his lesion is low. Unroof the fistulous track, as in C, Fig. 28-8. This will lead back to a normal anorectum, which you can open and dilate (D). Stitch his rectal mucosa to his skin. Finally, remove the mucous membrane lining the fistula.

POSTOPERATIVE CARE (all low lesions). Follow the child up carefully. The anus will probably need dilating at least once a week for a month or more. Warn the child's mother that toilet training will be delayed.

TRANSVERSE COLOSTOMY [s7]FOR HIGH ANORECTAL MALFORMATIONS PREPARATION. Pass a nasogastric tube and suck out the child's stomach frequently. Check his temperature, and put him in a warm bath if it is low. Put him on an electric blanket on the operating table, and bandage his arms and legs in cotton wool to conserve heat.

ANAESTHESIA. (1) Ketamine (A 8.5). (2) Give him a general anaesthetic, as in section 28.3. (3) Local anaesthesia as for the other operations described here.

INCISION. Make a short transverse incision in his right hypochondrium (see Section 9.5). Identify his transverse colon, from its connection by a short omentum to the greater curvature of his stomach.

CAUTION! Don't deliver his sigmoid colon.

Deliver his transverse colon through the wound, and pass a plastic rod under it through a hole in its mesentery, to make sure it remains outside his abdomen. Connect its ends with a rubber tube. Place some catgut sutures between the muscle of his gut and his abdominal wall.

Open the exteriorized loop immediately with a longitudinal incision. Suck out the contents of the proximal loop to decompress his abdomen. Refer him early if fluid loss from his colon is serious; otherwise refer him for definitive repair at 6 months.

DIFFICULTIES [s7]WITH ANORECTAL MALFORMATIONS If you are NOT SURE WHAT TO DO, remember that a fistula is a favourable lesion because there is already an opening between the gut and the outside. If it is narrow, dilate it. If it is wide, there is no need for an urgent colostomy unless: (1) he has signs of intestinal obstruction, or (2) his urinary tract is involved. If so, a colostomy is urgent.

If his ANAL MUCOSA EVERTS after you have operated on his imperforate anus, there is little you can do about it. This is not uncommon during the first three months.

If his ANUS BECOMES STENOSED, it will probably do so because it is fibrosed. Unfortunately, regular dilatation perpetuates the cause of the fibrosis. There may come a time when you will have to balance the softening that will follow dilating less often, with the widening that will follow dilating more often.

If he LOSES FLUID EXCESSIVELY FROM HIS COLOSTOMY, wait for 14 days, while giving him extra fluid to maintain a satisfactory fluid balance. His stools will usually become formed; if they don't, refer him.

If his PROXIMAL TRANSVERSE COLON PROLAPSES, this is a nuisance, but is not serious. You may be able to reduce it by pushing it back with vaseline gauze, or KY jelly, on a glove. If necessary, teach his mother to do this.

Fig. 28-8 ANAL AGENESIS WITH A FISTULA. A, a girl, showing the fistula opening close to her introitus. B, the cutback operation; note that the scissors point directly backwards, and are superficial. C, a fistula in a boy is being incised on a grooved director. D, the epithelium of the track has been removed, and his anal mucosa has been stitched to his skin. Adapted from Ravitch et al., ''Paediatric Surgery', Fig. 98-4. Yearbook Medical, with kind permission.